Microdata and schema.org

1. Microdata and schema.org

2. Basics • Microdata is a simple semantic markup scheme that’s an alternative to RDFa • Developed by WHATWG and supported by major search companies (Google, Microsoft, Yahoo, Yandex) • Like RDFa, it uses HTML tag attributes to host metadata • Vocabularies are controlled and hosted at schema.org

3. What is WHATWG? • Web Hypertext Application Technology Working Group • Community interested in evolving the Web with focus on HTML and Web API development • Ian Hickson is a key person, now at Google • Founded in 2004 by individuals from Apple, Mozilla and Opera after a W3C workshop • Concern about W3C's embrace of XHTML • Current work on HTML5 • Developed Microdata spec

4. http://whatwg.org/

5. HTML5 • Started by WHATWG as an alternative to XHTML, joined by W3C • A W3C candidate recommendation in 2012 (draft) • WHATWG will evolve it as a “living standard” • HTML5 ≈ HTML + CSS + js • Native support for graphics, video, audio, speech, semantic markup, … • Current partial support in majorbrowsers & extensions

6. Microdata • The microdata effort has two parts: • A markup scheme • Aset of vocabularies/ontologies • The markup is similar to RDFa in providing ways to identify subjects, types, properties & objects There’s also a standard way to encode microdata as RDFa • The sanctioned vocabularies are found at schema.org and include a small number of very useful ones: people, movies, etc.

7. An example <div> <h1>Avatar</h1> <span>Director: James Cameron (born 1954) </span> <span>Science fiction</span> <a href=”avatar-trailer.html">Trailer</a> </div>

8. An example: itemscope • An itemscope attribute identifies a content subtree that is the subject about which we want to say something <div itemscope > <h1>Avatar</h1> <span>Director: James Cameron (born 1954) </span> <span>Science fiction</span> <a href=”avatar-trailer.html">Trailer</a> </div>

9. An example: itemtype • An itemscope attribute identifies a content subtree that is the subject about which we want to say something • The itemtype attribute specifies the subject’s type <div itemscopeitemtype="http://schema.org/Movie"> <h1>Avatar</h1> <span>Director: James Cameron (born 1954) </span> <span>Science fiction</span> <a href=”avatar-trailer.html">Trailer</a> </div>

10. Microdata <-> RDF http://rdf-translator.appspot.com/

11. Microdata <-> RDF http://rdf-translator.appspot.com/

12. An example: itemtype • An itemscope attribute identifies a content subtree that is the subject about which we want to say something • The itemtype attribute specifies the subject’s type <div itemscopeitemtype="http://schema.org/Movie"> <h1>Avatar</h1> <span>Director: James Cameron (born 1954) </span> <span>Science fiction</span> <a href=”avatar-trailer.html">Trailer</a> </div> [ ] a schema:Movie .

13. An example: itemprop • An itemscope attribute identifies a content subtree that is the subject about which we want to say something • The itemtype attribute specifies the subject’s type • An itemprop attribute gives a property of that type <div itemscopeitemtype="http://schema.org/Movie"> <h1 itemprop="name">Avatar</h1> <span>Director: James Cameron (born 1954) </span> <span itemprop="genre">Science fiction</span> <a href=”avatar-trailer.html” itemprop="trailer">Trailer</a> </div>

14. An example: itemprop • An itemscope attribute identifies a content subtree that is the subject about which we want to say something • The itemtype attribute specifies the subject’s type • An itemprop attribute gives a property of that type <div itemscopeitemtype="http://schema.org/Movie"> <h1 itemprop="name">Avatar</h1> <span>Director: James Cameron (born 1954) </span> <span itemprop="genre">Science fiction</span> <a href=”avatar-trailer.html” itemprop="trailer">Trailer</a> </div> [ ] a schema:Movie ; schema:genre "Science fiction" ; schema:name "Avatar" ; schema:trailer <avatar-trailer.html> .

15. An example: embedded items • An itemprop immediately followed by another itemcope makes the value an object <div itemscopeitemtype="http://schema.org/Movie"> <h1 itemprop="name">Avatar</h1> <div itemprop="director"itemscopeitemtype="http://schema.org/Person"> Director: <span itemprop="name">James Cameron</span> (born <span itemprop="birthDate">1954</span>) </div> <span itemprop="genre">Science fiction</span> <a href="avatar-trailer.html" itemprop="trailer">Trailer</a> </div>

16. An example: embedded items [ ] a schema:Movie ; schema:director[ a schema:Person ; schema:birthDate "1954" ; schema:name "James Cameron" ] ; schema:genre "Science fiction" ; schema:name "Avatar" ; schema:trailer <avatar-trailer.html> . • An itemprop immediately followed by another itemcope makes the value an object <div itemscopeitemtype="http://schema.org/Movie"> <h1 itemprop="name">Avatar</h1> <div itemprop="director"itemscopeitemtype="http://schema.org/Person"> Director: <span itemprop="name">James Cameron</span> (born <span itemprop="birthDate">1954</span>) </div> <span itemprop="genre">Science fiction</span> <a href="avatar-trailer.html" itemprop="trailer">Trailer</a> </div>

17. schema.org vocabulary • Full type hierarchy in one file • 548 classes, 711 properties (5/4/14) • Data types: Boolean, Date, DateTime, Number (Float, Integer) Text (URL), Time • Objects: Rooted at Thing with two ‘metaclasses’ (Class and Property) and eight subclasses

18. http://www.schema.org/Recipe

19. Microdata as a KR language • More than RDF, less than RDFS • Properties have an expected type (range) • Might be a string • A list of types, any of which are OK • Properties attached ≥ 1 types (domain) • Classes can have multiple parents and inherit (properties) from all of them • No axioms (e.g., disjointness, cardinality, etc.) • No subPropertyOf like relation

20. Mixing vocabularies • Microdata is intended to work with just one vocabulary – the one at schema.org • Advantages • Simple, organized, well designed • Controlled by the schema.org people • Disadvantages: too simple, controlled • Too simple, narrow, mono-lingual • Controlled by the schema.org people • Schema.rdfs.org defines mappings between schema.org and popular RDF ontologies

21. Schema <-> RDF http://schema.rdf.org

22. Extending the schema.org ontology • http://www.schema.org/docs/extension.html • You can subclass existing classes • Person/Engineer • Person/Engineer/ElectricalEngineer • Subclass exisiting properties • musicGroupMember/leadVocalist • musicGroupMember/leadGuitar1 • musicGroupMember/leadGuitar2

23. Extension Problems • Do agreed upon meaning • Through axioms supported by the language (e.g., equivalence, disjointness, etc.) • No place for documentation (annotations, labels, comments) • Without a namespace mechanism, your Person/Engineer and mine can be confused and might mean different things

24. Serialization • Schema.org has a data model and serializations • Microdata is the original, native sterilization • RDFa is more expressive and works with the RDF stack • Everyone agrees that RDFa Lite is a good encoding: as simple as Microdata but more expressive • JSON-LD is also an accepted encoding • Search engines look for Microdata and RDFa encodings and are beginning to look for JSON-LD • Schema.org considers RDFa to be the “canonical machine representation of schema.org”

25. Conclusions • Microdata is a good effort by the search companies to use a simple semantic language • The semantics is pragmatic • e.g., expected types: A string is accepted where a thing is expected – “some data is better than none” • The real value is in • the supported vocabularies and • their use by Search companies • => Immediate motivation for using semantic markup